Diplomatic Dolphins: Special Call Diffuses Tension

Dolphins make a special diplomatic sound to diffuse tension
in difficult situations, scientists have found.

The news comes out of a new study that researchers say is
the most complete and detailed survey of the repertoire of sounds used by bottlenose
dolphins (Tursiops truncatus) to
communicate. The data was collected over years, starting in 2005, in the waters
off the Italian island of Sardinia.

Until now, scientists thought that dolphins' whistle sounds
were the most common and important noises they make. These melodious tonal
sounds allow dolphins to stay in contact with each other (especially mothers
and offspring), and to coordinate hunting strategies.

But in the new study researchers investigated so-called
burst-pulsed sounds, which are more complex and varied than the whistles. These
calls turn out to be vital to the animals'
social life, the scientists report.

The burst-pulsed sounds are used "to avoid physical
aggression in situations of high excitement, such as when they are competing
for the same piece of food, for example," said lead researcher Bruno Díaz
of the Bottlenose Dolphin Research Institute in Sardinia.

Bottlenose dolphins make longer
burst-pulsed sounds when they are hunting and at times of high aggression, he
said, and these calls allow each individual to maintain its position in the
hierarchy.

"Burst-pulsed sounds are used in the life of bottlenose
dolphins
to socialize and maintain their position in the social hierarchy in order
to prevent physical conflict, and this also represents a significant energy saving[s],"
Díaz said.

These strident sounds can be heard when multiple dolphins
are moving toward the same prey. The least dominant one will often move away in
order to avoid confrontation. Unlike human sounds, these dolphin noises can be
directed at a particular individual, rather than just sent out in all
directions.

"One dolphin can send a sound to another that it sees
as a competitor, and this one clearly knows it is being addressed," Díaz
said.

The study is detailed in the new book “Dolphins: Anatomy,
Behaviour and Threats” (Nova Science Publishers, 2010).

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